Re: Geckos, Servos, VFD and twitching on Z axis

Yup, servo is tuned. In fact, all is running fine now that we
installed the 10uf cap in the the 5V power line for the encoder on
the Z axis. We ran a test program over and over and the Z repeats in
position within .0005in. We just ran a 3D surface and the Z follows
right along with X and Y and produced a great looking surface. We
have ran the 3D program over and over again to show off and the
machine is functioning fine and has never missed a step.


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Torsten" <torsten@g...>
wrote:

>
> Could be the electrical interference from the VFD but
> have you try'd to tune the Servo?
> There should be 2 places to make adjustments to the
> Servos for proper tuning.
> A miss adjusted servo would likely twich a little at
> standstill.
> Check the documentation of the geckos.
> You would not notice a difference just switching the motor.
> Good Luck
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "yethdear0" <da-mack@e...>
> wrote:
> >
> > We tried the wire separation and isolation, we even swapped

motors

> > and encoders with the Y axis. We are at the mercy of the

machine's

> > construction. The Z axis servo is mounted right up front of the
> > spindle head. The spindle motor is directly behind that about

10"

> > away from the servo and encoder. The VFD we wanted mounted to

the

> > side of the spindle head for ease of use. We could have mounted

the

> > VFD in a cabinet behind the machine and rigged up a remote

keypad

> > for operation but we didn't realize that it would cause such

noise.

> >
> > The noise would result in a slight "twitch" of the Z axis

usually

> > causing a .005-.010 jump or error in the Z axis motion. As for

now,

> > everything seems to be working and repeating fine. I ran a

program

> > over and over and there were no position errors or twitches. As

for

> > other noises, the machine is located in a high school machine

shop.

> > It is surrounded by other machines, 3 phase and single phase and
> > machines powered from the some bus. We also have quite a few
> > machines with VFDs on them as well. So far, we have no noise
> showing
> > up. We are going to try some 3D contouring tomorrow. Any noise
> > produced by any of the axii will definitely show up then as a

divot

> > in the surface of the part. We have our fingers crossed.
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers

<rogersmach@y...>

> > wrote:
> > > I had the same crosstalk issues when I retrofitted my

Bridgeport.

> > I was able to just seperate the motor leads and encoder cables

to

> > rectify. It seems there should be a standard to eliminate cross-
> talk
> > and interference issues with encoders, or at least a more

absolute

> > fix and safeguard. I'm wondering what difference moving the 10

uf

> > cap on the encoder current a few inches away from the Gecko

made. I

> > dont have any caps on my encoder wiring and wondering if I need
> any.
> > Once I see a servo act extremely erradical and resolve it by

just

> > moving wires, It's not a very secure feeling for future

operation.

> > What else could possibly make it happen? Arcing in the spindle
> > motor? Noise from another piece of equiptment coming through the
> > line? Cell phone? The kids RC car? I think about this when I

have a

> > 1.25"dia. X .875"dia. shank Reamer buried 10" deep in a large
> > workpiece. Having 5hp at the ballscrews from the servos, that

would

> > be a disaster.
> > >
> > > Ron
> > >
> > > yethdear0 <da-mack@e...> wrote:
> > >
> > >
> > > Everything is shielded.
> > >
> > > By chance, we installed a 10 microfarad capacitor on the 5

volt

> > power
> > > wire that powers up our encoder and "Bigo!" all is great in

the

> > > universe. We also found out that the capacitor had to be
> installed
> > > within a few inches of the encoder. If we installed it at the
> > Gecko,
> > > it wouldn't help. All 3 axis repeat now on a travle indicator
> > > within .0005in.
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "vavaroutsos"
> > >
> > > wrote:
> > > >
> > > > Sounds to me like you are getting noise on your Z encoder.

Are

> > you
> > > > running single ended encoders, or differential with

converters?

> > Are
> > > > the encoder cables shielded? Did you use shielded VFD cable
> from
> > > the
> > > > VFD to the spindle motor? How are your ground connections
> > oriented?
> > > >
> > > > ~petev
> > > >
> > > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "yethdear0"
> > > > wrote:
> > > > >
> > > > > Hiya,
> > > > >
> > > > > We have an old Hurco knee mill that we have stripped and
> retro-
> > ed
> > > > > with a pc, CNCPro, Geckos and a Baldor VFD for the spindle
> > motor.
> > > > We
> > > > > just got it all up and running but have a problem with the

Z

> > axis
> > > > > servo or controller. Using a travel indicator on the Z

axis,

> > the
> > > > > movement is smooth and exact. We have the machine running

a

> > > program
> > > > > that move Z -.100" pauses for 1 second and then moves Z
> +.100"
> > > and
> > > > > then runs in a loop. When we turn on the VFD and the

spindle,

> > the
> > > Z
> > > > > axis seems noisy and the travel on the indicator will

start

> to
> > > > > drift .001" to .005" each time the program cycles. The

drift

> > is
> > > > > random, sometimes positive and sometimes negative but
> positive
> > > the
> > > > > majority of the time. When we slowed the motion to 1 ipm,

you

> > can
> > > > > see the motion twitch at random during the movement. This
> only
> > > > > happens when the spindle is running and only the on the Z
> > axis.
> > > We
> > > > > swapped out the servo motors with the Y axis and the

problem

> > > stayed
> > > > > with the Z axis controller. On the machine, the Z axis

servo

> > is
> > > > > mounted on the front of the spindle head of the machine,

the

> > > motor
> > > > > (5hp, 230V, 3ph,) is on the back of the head. The VFD (a

new

> > > > Baldor)
> > > > > is mounted on the side of the head about 6in from the Z
> servo.
> > We
> > > > > also dismounted the Z servo and located it away from the
> motor
> > > and
> > > > > VFD to test for magnetic flux or noise and it still

twitches.

> > We
> > > > > have also played with the gain and damping adjustment but
> > nothing
> > > > > there would correct the problem. The twitching is only in

Z,

> > all
> > > 3
> > > > > Geckos are getting their power from the same DC power

source

> > > which
> > > > > baffles us why the twitching is only on the Z axis. We are
> > also
> > > > > using new US Digital encoders. When we swapped servos

though,

> > we
> > > > > also swapped encoders and the twitching stays on the Z

axis.

> > We
> > > > also
> > > > > rerouted cables as far from our VFD and motor as possible

but

> > > still
> > > > > have the problem.
> > > > >
> > > > > Any suggestions or input will be greatly appreciated,

thanks.

> > >
> > >
> > >
> > >
> > >
> > > Addresses:
> > > FAQ: http://www.ktmarketing.com/faq.html
> > > FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> > > Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
> > >
> > > Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
> > > Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
> > > List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com,

wanliker@a...,

> > timg@k...
> > > Moderator: pentam@c... indigo_red@q... davemucha@j...
> [Moderators]
> > > URL to this group:

http://groups.yahoo.com/group/CAD_CAM_EDM_DRO

> > >
> > > OFF Topic POSTS: General Machining
> > > If you wish to post on unlimited OT subjects goto:
> > aol://5863:126/rec.crafts.metalworking or go thru Google.com to
> > reach it if you have trouble.
> > > http://www.metalworking.com/news_servers.html
> > >
> > > http://groups.yahoo.com/group/jobshophomeshop I consider this

to

> > be a sister site to the CCED group, as many of the same members

are

> > there, for OT subjects, that are not allowed on the CCED list.
> > >
> > > NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY
> POSTING
> > THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO
> EXCEPTIONS........
> > > bill
> > > List Mom
> > > List Owner
> > >
> > >
> > > Yahoo! Groups Links
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > ---------------------------------
> > > Do you Yahoo!?
> > > The all-new My Yahoo! – What will yours do?
> > >
> > > [Non-text portions of this message have been removed]